Abstract

We report the first measurements of the effective superfluid density of superconductor-ferromagnet (SC/FM) bilayers, where is the effective magnetic field penetration depth. Thin bilayers were sputtered in ultrahigh vacuum in quick succession onto oxidized Si substrates. Nb layers are thick for all samples, while Ni thicknesses vary from . determined from decreases rapidly as Ni thickness increases from zero to , then it has a shallow minimum at . behaves similarly, but has a minimum several times deeper. In fact, continues to increase with increasing Ni thickness long after has stopped changing. We argue that this indicates a substantial superfluid density inside the ferromagneticNifilms.

Received 28 September 2007Accepted 23 October 2007Published online 17 January 2008

Acknowledgments:

One of the authors (I.H.) gratefully acknowledges support of an OSU Presidential Fellowship. We are grateful to Professors Julia Meyer, A. Buzdin, and A. Golubov for many useful discussions and to Michael Hinton for technical assistance.